The use of stochastic methods as a way of circumventing this computational scaling was pioneered by the quantum state diffusion methods of Gisin and Percival [1]}. They showed that the solution to a large class of master equations could be modelled by the evolution of a stochastic Schrödinger equation with appropriately chosen stochastic forcing terms. Such calculations would result in a wavefunction that evolved in a non-deterministic manner, in response to the constant and random influence of the system's environment. The total history of a wavefunction calculated in such a way is known as a stochastic unravelling. In essence, these amount to samples in a Monte-Carlo numerical integration scheme of the path integral formulation, with each path corresponding to an unravelling, and can offer significant computational advantages over master equation methods [2]}. Additionally, conceptual insight into the interpretation of quantum mechanics with open systems offered by stochastic methods has been leveraged in proposals of modified theories of quantum mechanics such as the spontaneous collapse model of Ghirardi, Rimini and Weber [3]} and the subsequent continuous spontaneous localisation model of Ghirardi, Pearle, and Rimini [4]}. Extensions to relate these models to gravitation have also been proposed by Diosi [5]} and Penrose [6]}.
